FIG. 29 is an explanatory view illustrating the display states in the power-on state and in the power-off state of a common conventional display device. As illustrated in FIG. 29, a display device 101 in the power-on state shows an image in a display region A. A region (frame region B) called a frame or a bezel in the periphery of the display region A does not contribute to image display. In contrast, a display device 102 in the power-off state shows no image in the display region A, and the frame region B still does not contribute to image display.
Such common conventional display devices show only a black or gray screen when they show no image (for example, when they are in the power-off state), so that the devices are useless for users. On the contrary, large-size, difficult-to-move display devices (e.g., digital signage and television receivers) can be mere obstructions for users when they are in the non-display state because they occupy the same space either in the non-display state or in the display state. In particular, a large-size display device with a black screen in a bright room may not match the interior design, looking as if it is misplaced. In other words, such common conventional display devices have their own value only when they are in the display state.
Techniques to overcome this disadvantage have been suggested. For example, Patent Literatures 1 to 4 disclose a mirror display that includes a half mirror plate in front of a display device so that it can serve as a mirror when the display is in the non-display state. Such a mirror display can serve not only as a display, which is the original purpose, but also as a mirror. Specifically, when display light is emitted from the display device, the mirror display utilizes the display light to show an image in a region where the display light is emitted from the display device. When no display light is emitted from the display device, on the other hand, the mirror display reflects the outside light and serves as a mirror in a region where the display light is not emitted from the display device.
Examples of known optical components having a reflex function include multi-layer reflective polarizers, nanowire grid polarizers (e.g. Patent Literatures 5 and 6), and circular-polarized-light separation sheets (e.g. Patent Literature 7) utilizing selective reflection of cholesteric liquid crystal.